Method and apparatus for synchronizing magnetos



Jan. 11, 1944. J. R. LYMAN 2,338,861

METHOD AND APPARATUS FOR SYNCHRONIZING MAGNETOS Filed NOV. 10, 1941 w /0 7 If /0 mam/mow 2 /o 6 L A? INVENTOR 707M112 Lyme/v ATTORNEYS Patented Jan. 11, 1944 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR SYNCHRO- NIZING MAGNETOS This invention relates to a method and apparatus for synchronizing magnetos. It has special application in the testing of an aeroplane engine equipped with two magnetos, the breaker points of which should be regulated to open simultaneously or in a predetermined timed relationship. It is therefore specifically related to determining the opening times of these points so that adjustments may be made to cause each set to open in the desired timed relation.

I The primary object of my invention is to test the magnetos without any possibility of the motor starting during such testing. In testing an aeroplane engine to synchronize the two sets of magneto breaker points a mechanic turns the propeller by hand causing lobed magneto cam shafts 'to rotate in the breaker-arm supports or plates and cause each set of points to separate. Another mechanic using a device attached to each magneto assembly for visibly indicating the separation of the points, can then make the necessary corrections in each magneto to have them open at the desired time as the first mechanic continues to turn the propeller.

With the devices now known to me. and in use at the present time for visibly indicating when separation of points occurs there is present a very great danger that the mechanic rotating the propeller will turn the motor over with suflicient rapidity to start the engine. with the result that the propeller suddenly spinning may cause him severe bodily injury or loss of life. The danger arises from the nature of these prior testing devices which require that the magneto controlling switch be in "011 position in order to operate the visible indicators. As will be readily appreciated by the man skilled in the art this means that the wires leading to the switch from opposite ends of the primary coil are not connected together so that the primary coil of the magneto is enabled if the shaft of the magneto is rotated, to energize the secondary coil and possibly operate the engine.

My invention is directed to elimination of any danger of the motor starting by conducting the test with the magneto control switch in off position so that the aforementioned wires leading to the switch will be electrically connected and thus will short circuit the primary coil while the propeller is being turned and prevent the secondary coil from being energized.

To obtain this object I have utilized the natural frequency of a circuit in the magneto assembly composed of the Wires leading from the ends of the primary coil closed by; the switch and the contacting breaker points of the magneto. First coupling this circuit to the grid of a vacuum tube, I then tune a second circuit connected to the plate of the tube so that, when the breaker points change their relationship either by opening or closing, the tube is brought into a more perfect state of oscillation, By providing a suitable indicating means in the plate circuit I may then take advantage of the shift in the oscillatory characteristics of the system by setting the indicator to reflect this shift as the relationship of the points is altered. During the time the points are opening and closing and nomatter how rapidly for the purposes of the test, the magneto control switch remains closed. By testing each setof points at the same time the magnetos may then be adjusted to have the indicators reflect the" desired change in both sets;

The manner in which this result is obtained will be apparent in the following description accompanied by' the drawing, in which:

Fig. l is a plan view of a magneto breaker plate;

Fig. 2 is a diagram showing the circuit of my apparatus as attached to the breaker plate assembly circuit of the magneto;

Fig. 3* is a diagram of a modification of the indicating means; and

Fig. 4' is a simplified schematic diagram of the magneto assembly circuit.

In Fig. 1 there is illustrated only as muchof the magneto breaker plate assembly as is necessary for an understanding of the operation of my invention. It is a standard part of a magneto in an aeroplane engine. As there seen a supporting or breaker plate I is shown having mounted thereon the breaker points consisting of fixed point 2- and movable point 3. The fixed point 2 is mounted on and grounded to plate I by an adjustable support 4 to regulate the degree of opening of the points as is well known. A usual breaker arm 5 pivoted at 6 andprovi'ded with a spring I held at one end on a plate stud 8 is mounted to open and close the pointsby moving point 3 out of contact with point 2 as a camon shaft I is rotated in opening 9 of the plate. The movable point 3- is fixed to a spring strip 3' fastened to a bolt lilwhich-.i'sinsulated from the plate i by an insulating strip construction I 0 mounted on the plate. The spring strip 3- returns the points 2 and 3 to the position of Fig. 1 when arm 5 rides" onto the low point of the cam. Bolt- I0 is connected by abrace II- to the wire l2 which leads to the primary coil (not shown). Bolt It! also leads to the magneto control switch on the instrument panel of the motor by stud I3 through a device not here shown as it forms no part of my invention. A condenser I6 is also connected. by a lead I4 to bolt I and through the insulation to point 3. It is suitably mounted on the plate as shown and is to avoid sparking in the points as is well known. The circuit established by the various connections of this assembly is shown in the diagram of Fig. 2 at the left, the numeral Il designating the control switch and I5 designating the grounding connection to complete the short circuiting switch line back to plate I, not shown in Fig. 1. The breaker plate I is shown grounded at I8. Switch II governs the switch circuit and operates when closed to connect the stud I3 to the frame of the aeroplane through grounding connection I5 and cut the motor dead by short circuiting the points, thus preventing, as will be readily understood, the energizing of the secondary magneto coil (not shown). It is a primary feature of this invention as I have previously stated that the switch is closed while conducting the test so that under no circumstances can the engine be started.

The circuit in the magneto assembly to which I apply the apparatus of my invention can be generally represented by the switch wires and the breaker points connected thereto. This is shown enclosed by the dotted line B of the simplified schematic diagram of Fig. 4. I have not included the condenser I6 and primary coil I9 in this circuit since in actual tests with a breaker plate I have found that the connection of the coil creates no appreciable difference in the natural frequency found to exist When it is not in the circuit. And no appreciable effect can be observed when the condenser is taken out of the circuit. Therefore, for the purposes of simplification I may describe the effective circuit in this magneto assembly as that enclosed by the dotted line. It will be readily understood from this diagram that the natural frequency of this circuit will be disturbed when the points 2 are separated.

To take advantage of this disturbance in the natural frequency of the above mentioned circuit, I have employed apparatus shown in the diagram of Fig. 2 as a preferred form of my testing circuit. The test lead wires and 2| are clipped respectively to the magneto assembly on stud 8 and stud I3, the wire 20 at one end being connected through the plate I to the breaker point 2 and at the other end being grounded at 22 through shielding 23 surrounding wire 2|. Wire H is connected through stud I3 to point 3 and being shielded as is common leads at the other end to the grid of a simple vacuum tube 25. I The filament circuit of tube 25 is perfectly standard and is therefore not described other than'to point out that the source of energy is the usual A battery 26.

The plate of vacuum tube 25 is connected in series with a resonant circuit, denominated generally by the numeral 21, and a milliammeter 28. The source of plate supply for the vacuum tube 25 is B battery 32. A variable condenser 29 in circuit 21 permits the tuning of the plate circuit to match it approximately with the grid circuit. This may be observed in the milliammeter as will be later described. A rheostat 30 and battery 3i coupled to the milliammeter as shown also enables the latter to be adjusted for testing as will also be hereinafter explained.

It will be understood from the object of the test that is being conducted that the device above described as attached by the wires 20 and 2I to the assembly will be duplicated in connection with the second magneto breaker plate assembly in the engine. It has been deemed sufficient for the purposes of this disclosure to show the single circuit attached to one magneto.

During testing the device is operated as follows: The wires 20 and 2I are clipped to the contact points as indicated. The switch I! is turned off establishing the circuit described in Figs. 1 and 2 and shown simply in Fig. 4. The current is set up in the vacuum tube 25 by connecting the A battery 26 and B battery 32 to the filament and plate of the tube.

The variable condenser 29 in the resonant circuit'21 is then tuned to approximately balance the circuits on each side of the tube.

Since, as will be apparent, the meter 28 can only be used forshowing an increase and decrease in plate current, the tuning of the condenser should vary the resonance only enough to allow the needle of the meter 28 to indicate an observable variation in the flow of current through the plate circuit. The opening and closing of the points 2 and 3 will then be reflected in the swing of the milliammeter needle to a new position as the changing relationship of the points varies the amount of current by varying the degree of similarity between grid and plate circuits. In order to obtain a greater swing of the needle the rheostat 30 and battery 3I coupled to the milliammeter may be used to set up a counter-electro-motive force acting against the current flowing through the meter and thus cause the needle to point to any desired extreme on the meter dial. The sharp definition that can be obtained through the use of the rheostat and battery enables me to set the condenser in the device so that once regulated it needs no further adjustment when testing magneto assemblies having generally similar characteristics. Slight variations in each assembly can be overcome by operating the rheostat when the test lead wires are connected.

Th operation of this device is dependent on the fact that the similarity in the electrical constants of the grid and plate circuits is disturbed as the points are opened or closed. Since the amount of current flowing in the circuit is least when the degree of oscillation is greatest, the change in the grid circuit by the opening and closing of the points will change the degree of oscillation in the entire circuit. This change in oscillatory characteristics is reflected in the meter needle as it immediately indicates a greater or less flowing of current therethrough the moment the grid circuit changes its characteristics.

Thus, to continue the description of the operation, assuming that the plate circuit has been tuned to enable the tube to oscillate more perfectly when the points 2 and 3 are opened, the rheostat is regulated to have the meter needle point to the highest reading on the dial. It is also assumed that the breaker points 2 and 3 are closed, a condition that may be observed when the test lead wires 20 and 2! are clipped on the plate I at the places indicated. A mechanic then turns the propeller rotating the magneto cam shaft in the breaker plate I and causing the points to open. As they open, the test circuit goes into a more perfect degree of oscillation thereby sending less current through meter 28 causing the needle to swing to a lower point on the dial. Since the breaker points of the second magneto assembly in the motor are also connected with a similar device the milliammeter needle in that device should likewise swing to a lower dial reading. Should the needles in the meters in the two devices fail to move at the predetermined time, thereby showing that the points are not separating as desired, adjustments can then be made in the'magnetos to have a suitable reaction on the two dials.

.It will be appreciated that since during the test the control switch is in off position, a motor cannot possibly start as the magneto cam shafts are rotated and therefore a mechanic can turn by hand the propeller of an aeroplane quickly and as often as is necessary to make corrections and have the points synchronized.

In Fig. 3 I have shown an arrangement to be used as a modification of the milliammeter indicating means. In that drawing a resistor 33 in the wire leading from the B battery 32 is shown with a neon lamp 3Q connected to the circuit at 35. In this arrangement with the plate circuit tuned as I specified above so that more perfect oscillation occurs as the points open, the lamp is lighted when the points are closed. When they are opened by the turning of the cam shaft, the lamp is extinguished. This results from the fact that as the current decreases in the line through the resistor the voltage at point 35 decreases and lamp 34 goes out.

It will be seen that when the plate circuit has been tuned so that more perfect oscillation occurs when the points are closed, then the needle of meter 28 would indicate an increase in current flow as the breaker points are opened since the circuit is then oscillating less efiiciently. This means that the operator Would regulate the rheostat to have the meter needle point to the lowest reading on the dial. In the case of the neon lamp the lighting of the lam-p would occur as the current became stronger, that is, as the points were opened.

It is obvious that the operator of my device may adapt the instrument as he desires, the object being to observe a variation in characteristics in the test circuit when the points 2 and 3 are separated. Having disclosed this method of visibly indicating the change in characteristics it will be apparent to the man skilled in the art that many variations in the apparatus for setting up the circuit are possible so that the desired result may be achieved. For example, the variable condenser 29 might be connected in other relations to the tube 25 and still affect the coil in resonant circuit 21, or use may be made of relays as may be desired.

It will be understood from the above description of my invention as applied to a magneto, and particularly in connection with the aeroplane magneto, that this device may be operated to indicate the electrical opening and/or closing of any device acting as an interrupter (here specifically the breaker points 2 and 3) Where said device acting as an interrupter is paralleled either remotely or adjacent thereto by a short circuiting means (herein the switch controlled ignition connections l3 and I5) I therefore do not desire to limit my invention necessarily to its specific application as applied to these magnetos although this problem was the prime motive for my invention.

I claim:

1. A method of indicating the opening and closing of magneto breaker points when the magneto control switch is closed, which method consists in attaching to a magneto assembly circuit, having therein the breaker points and said switch wires closed by the switch, a testing circuit adjusted to cause oscillation, when attached, at a frequency near the frequency of the assembly circuit and including means to indicate a change in oscillation, then causing said breaker points to open and close to thereby Vary the oscillatory characteristics of the testing circuit.

2. A method of indicating the opening and closing of magneto breaker points when the magneto control switch is closed, which method consists in causing oscillation in that circuit of the magneto assembly which includes the closed switch wires and said breaker points connected therewith, then indicating the shift in oscillatory characteristics of the circuit as the points are opened and closed by rotation of the magneto shaft.

3. The method of synchronizing the breaker point opening times of two magnetos in one engine for their relative operation, which method consists in closing the magneto control switches to make a circuit in each magneto assembly of the closed switch wires and breaker points connected thereto, then causing said circuits each to oscillate in a circuit at approximately its natural frequency, rotating the magneto cam shafts to open and close said breaker points, then indicating the shift in the degree of oscillatory efficiency in each circuit as the points open and close, and adjusting said magnetos to indicate a desired relative shift in oscillation as the shafts are rotated.

4. Apparatus for determining the opening of magneto breaker points when the magneto is short circuited to prevent the secondary coil from being energized, said apparatus including a vacuum tube, means to connect the grid of said tube to the magneto assembly, means to vary the resonance of the plate circuit, an indicating device to register a shift in oscillatory characteristics of the circuit, and a source of current supply for said apparatus.

5. Apparatus for determining the opening of magneto breaker points when the control switch Wires are short circuiting said magneto, said apparatus comprising a vacuum tube, mean to connect the grid of said tube to a magneto assembly circuit including the closed control wires and breaker points, means connected to the plate of said tube to adjust the resonance of the plate circuit, a neon lamp connected to the plate circuit in series with said means, a resistor in said circuit, and a source of current supply for said circuit, said lamp being lighted and extinguished as the oscillatory characteristics of said circuit are changed.

6. A method of indicating the opening and closing of an electrical circuit interrupter which has its terminals joined together by a short circuiting means and which is connected in series with additional electrical circuits, th energization of which in the absence of said short circuiting means is controlled by said circuit interrupter, which method consists in establishing oscillation in the circuit comprising said interrupter and short circuiting means, then indicating the change in the electrical characteristics of th circuit as the circuit interrupter is operated.

'7. A method of indicating the opening and closing of magneto breaker points when the magneto control switch is closed, which method consists in establishing oscillation in that circuit of the magneto assembly which includes the closed of the short circuit through the closed switch and breaker points, a plate circuit of predetermined resonance which includes the anode and cathode of the tube and an indicating device in the plate circuit to detect changes in electrical characteristics of the circuit set up by a change in the circuit characteristics of said. magneto assembly, the filament and plate of said tube being provided with a source of current supply.

JOHN R. LYMAN. 

